Difficulties with attention and concentration are some of the most common complaints among individuals with Posttraumatic Stress Disorder (PTSD). These difficulties can came either in the form of problems with sustained attention as evidenced by concentration problems or in the form of biases in selective attention as evidenced by symptoms such as hypervigilance. While some investigators suggest that these attentional disturbances are pervasive in nature, others argue that the difficulties are selective and depend on internal states and external circumstances. This project aims to conduct a multi-method examination of sustained and selective attention in PTSD using self-report, behavioral, and event-related potential (ERP) measures. The study is designed to investigate two factors, affective priming and stimulus novelty, and their independent and potentially interactive affect of attention and concentration in PTSD. The proposed studies arise from predictions based on recent information processing theory and current research ongoing at this lab that suggest both affective priming and the stimulus novelty impact on an individual with PTSD's ability to allocate attention appropriately. Study 1 will investigate differences in sustained and selective attention in 90 individuals exposed to combat. Analyses will be based on three primary groups: veterans with PTSD and comorbid depression, veterans with PTSD and comorbid anxiety, and veterans with no Axis I or Axis II diagnosis. Study 2 will look at these differences in 90 individuals who have been exposed to a single motor vehicle accident who will be separated into these same three groups. Participants in both studies will undergo a series of self- report measures, behavioral tasks, and ERP protocols particularly sensitive to attentional processing. All these measures will be given under the four conditions that result from the interaction of affective priming (neutral versus trauma-relevant imagery) and novelty (familiar versus novel). It is our hypotheses that individuals with PTSD will reveal a pattern of responses across electrophysiological and behavioral measures that suggest an enhanced processing of novel, distracting stimuli with concurrent deficits in the processing of task-related stimuli. These biases will be exacerbated for subjects with PTSD in affective prime conditions. This work will add significantly to our current knowledge because of its multi-method assessment, it's utilization of electrophysiological indices of encoding, and its basis in testable information processing theory.